Attached for filing are exhibits containing interactive data format risk/return summary information that mirrors the risk/return summary information included
in a supplement to the Class A, Class B and Class C Prospectus and to the Class I and Class R Prospectus, each dated March 1, 2013, as amended August 5, 2013, for Calamos High Income Fund, a series of Calamos Investment Trust, filed
with the Securities and Exchange Commission on October 31, 2013 (Accession No. 0001193125-13-420628), the purpose of which was to reflect a change in the index used as the Funds benchmark.

The date the document was made available and submitted, in CCYY-MM-DD format. The date of submission, date of acceptance by the recipient, and the document effective date are all potentially different.

The table captioned “Average Annual Total Returns for the Periods Ended 12.31.12” for the Calamos High Income Fund on Page 50 of the Class A, B and C Prospectus shall be replaced in its entirety as follows:

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED 12.31.12

INCEPTIONDATE OF CLASS

ONE YEAR

FIVE YEAR

TEN YEAR

SINCEINCEPTION

Class A

8.2.99

Load Adjusted Return Before Taxes

5.99

%

5.35

%

7.74

%

6.58

%

Load Adjusted Return After Taxes on Distributions

3.72

%

3.11

%

5.30

%

4.18

%

Load Adjusted Return After Taxes on Distributions and Sale of Fund Shares

4.13

%

3.29

%

5.29

%

4.22

%

Class B

12.21.00

Load Adjusted Return Before Taxes

5.45

%

5.27

%

7.61

%

7.46

%

Class C

12.21.00

Load Adjusted Return Before Taxes

9.46

%

5.59

%

7.47

%

7.20

%

BofA Merrill Lynch BB-B US High Yield Constrained Index

14.59

%

9.10

%

9.30

%

7.10

%

Credit Suisse High Yield Index

14.72

%

9.53

%

10.25

%

7.84

%

The BofA Merrill Lynch BB-B US High Yield Constrained Index contains all of the securities included in The BofA Merrill Lynch US High Yield Index rated BB1 through B3, based on an average rating by Moody’s, S&P and Fitch, but caps issuer exposure at 2%. The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

The table captioned “Average Annual Total Returns for the Periods Ended 12.31.12” for the Calamos High Income Fund on page 50 of the Class I and R Prospectus shall be replaced in its entirety as follows:

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED 12.31.12

INCEPTIONDATE OF CLASS

ONE YEAR

FIVE YEAR

TEN YEAR

SINCEINCEPTION

Class I

3.1.02

Load Adjusted Return Before Taxes

11.50

%

6.65

%

8.55

%

7.83

%

Load Adjusted Return After Taxes on Distributions

9.02

%

4.30

%

6.00

%

5.31

%

Load Adjusted Return After Taxes on Distributions and Sale of Fund Shares

7.72

%

4.34

%

5.94

%

5.29

%

Class R

3.1.07

Load Adjusted Return Before Taxes

10.98

%

6.12

%

—

5.64

%

BofA Merrill Lynch BB-B US High Yield Constrained Index

14.59

%

9.10

%

9.30

%

8.68

%

Credit Suisse High Yield Index

14.72

%

9.53

%

10.25

%

9.70

%

The BofA Merrill Lynch BB-B US High Yield Constrained Index contains all of the securities included in The BofA Merrill Lynch US High Yield Index rated BB1 through B3, based on an average rating by Moody’s, S&P and Fitch, but caps issuer exposure at 2%. The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

The table captioned “Average Annual Total Returns for the Periods Ended 12.31.12” for the Calamos High Income Fund on Page 50 of the Class A, B and C Prospectus shall be replaced in its entirety as follows:

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED 12.31.12

INCEPTIONDATE OF CLASS

ONE YEAR

FIVE YEAR

TEN YEAR

SINCEINCEPTION

Class A

8.2.99

Load Adjusted Return Before Taxes

5.99

%

5.35

%

7.74

%

6.58

%

Load Adjusted Return After Taxes on Distributions

3.72

%

3.11

%

5.30

%

4.18

%

Load Adjusted Return After Taxes on Distributions and Sale of Fund Shares

4.13

%

3.29

%

5.29

%

4.22

%

Class B

12.21.00

Load Adjusted Return Before Taxes

5.45

%

5.27

%

7.61

%

7.46

%

Class C

12.21.00

Load Adjusted Return Before Taxes

9.46

%

5.59

%

7.47

%

7.20

%

BofA Merrill Lynch BB-B US High Yield Constrained Index

14.59

%

9.10

%

9.30

%

7.10

%

Credit Suisse High Yield Index

14.72

%

9.53

%

10.25

%

7.84

%

The BofA Merrill Lynch BB-B US High Yield Constrained Index contains all of the securities included in The BofA Merrill Lynch US High Yield Index rated BB1 through B3, based on an average rating by Moody’s, S&P and Fitch, but caps issuer exposure at 2%. The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

The BofA Merrill Lynch BB-B US High Yield Constrained Index contains all of the securities included in The BofA Merrill Lynch US High Yield Index rated BB1 through B3, based on an average rating by Moody’s, S&P and Fitch, but caps issuer exposure at 2%. The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

The table captioned “Average Annual Total Returns for the Periods Ended 12.31.12” for the Calamos High Income Fund on page 50 of the Class I and R Prospectus shall be replaced in its entirety as follows:

AVERAGE ANNUAL TOTAL RETURNS FOR THE PERIODS ENDED 12.31.12

INCEPTIONDATE OF CLASS

ONE YEAR

FIVE YEAR

TEN YEAR

SINCEINCEPTION

Class I

3.1.02

Load Adjusted Return Before Taxes

11.50

%

6.65

%

8.55

%

7.83

%

Load Adjusted Return After Taxes on Distributions

9.02

%

4.30

%

6.00

%

5.31

%

Load Adjusted Return After Taxes on Distributions and Sale of Fund Shares

7.72

%

4.34

%

5.94

%

5.29

%

Class R

3.1.07

Load Adjusted Return Before Taxes

10.98

%

6.12

%

—

5.64

%

BofA Merrill Lynch BB-B US High Yield Constrained Index

14.59

%

9.10

%

9.30

%

8.68

%

Credit Suisse High Yield Index

14.72

%

9.53

%

10.25

%

9.70

%

The BofA Merrill Lynch BB-B US High Yield Constrained Index contains all of the securities included in The BofA Merrill Lynch US High Yield Index rated BB1 through B3, based on an average rating by Moody’s, S&P and Fitch, but caps issuer exposure at 2%. The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

The BofA Merrill Lynch BB-B US High Yield Constrained Index contains all of the securities included in The BofA Merrill Lynch US High Yield Index rated BB1 through B3, based on an average rating by Moody’s, S&P and Fitch, but caps issuer exposure at 2%. The BofA Merrill Lynch BB-B US High Yield Constrained Index is provided to show how the Fund’s performance compares with the returns of an index of securities similar to those in which the Fund invests.

This item represents Average Anuual Total Returns. If a Multiple Class Fund offers a Class in the prospectus that converts into another Class after a stated period, compute average annual total returns in the table by using the returns of the other Class for the period after conversion.